Browsing by Subject "Oxidativer Stress"

Now showing 1 - 2 of 2

Analysis of phytotoxicity and plant growth stimulation by multi-walled carbon nanotubes
(2016) Zaytseva, Olga; Neumann, Günter
Nanotechnology is a rapidly expanding area of science and technology, which has gained a great interest due extraordinary properties of nanomaterials with numerous potential fields for practical application. Meanwhile, carbon nanotubes (CNTs) are among the ten most-produced engineered nanomaterials worldwide with applications in automotive industry, building and construction, electronics, and many other industrial sectors, showing also a great potential for integration into environmental and agricultural applications. However, during the last decade it has been demonstrated that nanomaterials can exert significant and extremely variable effects also on living organisms. In higher plants, both, positive and negative responses on growth and development have been reported but the related mechanisms are still not entirely understood. This study presents a systematic assessment of CNT effects on representative crops under standardized conditions with special emphasis on interactions with plant nutrition. After the introductory background (Chapter 1), presenting a comprehensive literature review on carbon nanomaterials with special emphasis on plant responses, environmental and agricultural applications, Chapter 2 describes the impact of selected multi-walled carbon nanotubes (MWCNTs) on seed germination and early seedling development of different crops (soybean−Glycine max, maize−Zea mays, and common bean−Phaseolus vulgaris). In face of highly variable plant responses to CNT treatments reported in the literature, the study was designed as a systematic analysis under standardized growth conditions, dissecting the effects of one single type of MWCNTs, depending on plant species, MWCNT dosage, duration of exposure to MWCNT treatments, and plant-developmental stage, including imbibition, germination and seedling development. Short-term seed treatments (36 h) with MWCNTs reduced the speed of water uptake particularly by soybean seeds, associated with an increased germination percentage and reduced formation of abnormal seedlings. However, during later seedling development, negative effects on fine root production were recorded for all investigated plant species. Inhibition of root growth was associated with reduced metabolic activity of the root tissue and a reduction of nitrate uptake, which could be mainly attributed to the smaller root system. The results demonstrated that even under standardized growth conditions largely excluding external factors, plant responses to MWCNT exposure exhibit differences, depending on plant species but also on the physiological status and the developmental stage of individual plants. Soybean was selected as a model plant for further studies since both, positive and negative effects of the same dose of MWCNTs (1000 mg L-1) could be observed even in the same individual plants. Chapter 3 investigates effects of short-term soybean seed exposure (36 h) to MWCNTs on seedling development, depending on the nutrient availability of the substrate. At 8 DAS stunted growth and poor fine root production were first detectable in seedlings germinating on moist filter paper without additional nutrient supply. This effect was preceded by reduced metabolic activity of the seedling tissues detectable by vital staining already at 2 DAS. Root growth inhibition was a long-lasting effect, detectable in soil culture up to 38 DAS. More detailed investigations revealed zinc (Zn) deficiency as a major growth-limiting factor. The growth of affected soil-grown plants was recovered by foliar application of ZnSO4 or by cultivation in nutrient solution supplied with soluble ZnSO4. A more detailed investigation of the physiological mechanisms related with the inhibitory effects of MWCNTs on plant growth is presented in Chapter 4. Oxidative stress was identified as a major factor determining MWCNT-induced root growth inhibition in soybean, demonstrated by recovery of root development after external supplementation with antioxidants. Induction of oxidative stress by MWCNT application was detectable already after the 36 h imbibition period particularly in the tips of the radicle as indicated by accumulation of superoxide anions, reduced triphenyltetrazolium chloride vital staining, and induction of superoxide dismutase activity. The expression pattern of the oxidative stress indicators coincided with preferential accumulation of MWCNTs in the cells of the root tip and was reverted by external application of proline as antioxidant. MWCNT-induced plant damage could be reverted by external supplementation of micronutrients (Zn, Cu, Mn) as important cofactors for various enzymes involved in oxidative stress defense (SOD, biosynthesis of antioxidative phenolics). Accordingly, SOD activity increased in seedling roots after Zn supplementation. During germination, the CNT treatments inhibited particularly the Zn translocation from the cotyledons to the growing seedling, and CNTs exhibited a selective adsorption potential for Zn and Cu, which may be involved in internal immobilization of micronutrients. Therefore, this study demonstrated for the first time that phytotoxicity of CNTs is linked with disturbances of micronutrient homeostasis during seedling development. Implications for environmental phytotoxicity assessment of MWCNTs and their potential applications in agriculture are discussed in a final overview presented in Chapter 5.
Cellular stress regulates fibroblast growth factor 23 (FGF23) und αklotho
(2023) Münz, Sina; Föller, Michael
Cellular stress is defined as the impairment of regular cell function by internal or external stimuli including critical temperatures, energy deficiency, infections, mechanic injury, or chemical noxae. The present thesis aims to investigate the influence of cellular stress on the expression of FGF23 and αklotho. FGF23 is predominantly produced in bone and regulates the phosphate excretion in the kidney. Thereby, αklotho functions as a co-receptor for FGF23. By binding to the FGF receptor-αklotho complex, FGF23 reduces the reabsorption of phosphate from the tubular lumen by decreasing the abundance of sodium-phosphate co-transporters. Furthermore, FGF23 decreases the synthesis of 1,25(OH)2D3, active vitamin D, and increases its degradation. 1,25(OH)2D3 is a regulator of intestinal phosphate absorption and therefore, FGF23 additionally reduces dietary phosphate uptake. Chronically elevated FGF23 is associated with numerous disorders such as kidney disease or CVD. Beside its function as a co-receptor of FGFR, αklotho has many beneficial FGF23-independent functions. It has originally been identified as an anti-aging hormone, as a loss-of-function mutation in the αklotho gene causes numerous aging-like symptoms such as vascular and tissue calcification, osteoporosis, sterility, and an early death. The present papers investigated the influence of cytostatic drugs cisplatin, paclitaxel, and doxorubicin as well as apoptosis inducers PAC-1 and serum depletion on the regulation of FGF23 and αklotho. In UMR106 rat osteoblast-like osteosarcoma cells, a 24 or 48 h-treatment with cisplatin, doxorubicin, PAC-1, or serum reduction and depletion significantly up-regulated Fgf23 expression. Under serum depletion, also FGF23 protein secretion was increased. In addition to FGF23, cisplatin and doxorubicin also increased gene expression of pro-inflammatory cytokine Il6 hinting at the presence of necrotic cell death. By inhibiting Il-6 membrane receptor gp130 it has been shown, that FGF23 stimulation partially depended on IL-6 signaling. The stimulation of FGF23 by inflammatory mediators including IL-6, TNFα, TGF-β, or IL-1β has already been reported by others. Furthermore, inflammatory diseases such as rheumatoid arthritis, CKD, or inflammatory bowel disease are associated with excess FGF23 serum concentrations. In this regard, we investigated gene expression and activation of the transcription factor NFκB, which regulates numerous inflammatory functions. Cisplatin and doxorubicin increased the expression of NFκB subunit Rela and cisplatin also stimulated the phosphorylation of NFκB. Independently, NFκB inhibitors wogonin and withaferin A attenuated cisplatin-mediated stimulation of FGF23 indicating, that FGF23 excess was in part promoted by NFκB signaling. These investigations confirmed a strong impact of cisplatin or doxorubicin-induced inflammation on FGF23 synthesis, whereas PAC-1 and serum depletion have reported to directly induce apoptosis, which is commonly not associated with inflammation. Known factors, induced by all cytotoxic substances used here, are the formation of ROS and activation of HIF1α. Both are positive regulators of FGF23, leading to the conclusion, that cellular stress might regulate FGF23 via HIF1α or oxidative stress. FGF23 excess results in increased bone resorption and suppressed bone formation. Likewise, also chemotherapeutic drugs and serum deficiency reduce bone density. Therefore, the stimulation of FGF23 may cause or further stimulate bone resorption. In paper 2, the influence of the cytostatic drugs cisplatin, paclitaxel, and doxorubicin as well as apoptosis inductors PAC-1 or serum depletion on αklotho expression in renal MDCK, NRK-52E, and HK-2 cells has been investigated. In fact, all cytotoxic compounds stimulated gene expression of αklotho while decreasing cell proliferation and viability. By using a combined apoptosis and necrosis assay, we confirmed the induction of apoptosis but also necrosis to a variable extent. Additionally, the transcriptional regulation of apoptotic proteins of the BCL-2 family was assessed and confirmed apoptosis stimulation. Transcription factor PPARγ is a known positive regulator of αklotho. In MDCK cells, we detected a significant influence of cisplatin-mediated stimulation of PPARγ mRNA on the αklotho increase. Furthermore, cisplatin, doxorubicin, PAC-1, and serum deprivation also up-regulated FGFR production in MDCK cells. In cancer cells, overexpression of FGFR is associated with enhanced resistance against chemotherapeutic drugs. Consequently, αklotho and FGFR1 stimulation may be a protective mechanism to prevent hyperphosphatemia during diseases. However, human HK-2 cells treated with cisplatin, paclitaxel, doxorubicin, or serum depletion significantly down-regulated αklotho expression and protein secretion. PAC-1 did not change the expression or production of αklotho in HK-2 cells, which might be explained by the minor effect of PAC-1 on non-carcinogenic cells lacking an overexpression of procaspase-3. The differential regulation of αklotho in MDCK and NRK-52E versus HK-2 cells by cytotoxic stress might have numerous causes. For instance, there is evidence of an increased sensitivity of HK-2 cells to stress stimuli but a better comparability to the animal model. However, immortalized cell lines can not completely reflect the conditions of native tissue especially with regard to cell death. Furthermore, the species, sex or age of the donor organism as well as passage number of the cells and drug transporter expression might impact αklotho regulation. Additionally, the mode of cell death determined by intracellular ATP homeostasis and its regulation of AMPK might play an important role in αklotho regulation. However, all these theories need to be further addressed. In summary, inflammation, ROS formation, or the activation of HIF1α are all reported to correlate in a negative manner with αklotho production or serum levels. αklotho down-regulation may be a tool to increase cell proliferation or prevent hypophosphatemia. In contrast, AMPK activation by intracellular ATP restriction may positively regulate αklotho to promote cell protection and avoid hyperphosphatemia.